MDEV-12059: Assertion `precision > 0' failed with a window function or window aggregate function

Pass the unsigned flag from the Item_sum to the window function

mysql-test/r/win.result

@@ -3798,5 +3798,15 @@ SELECT FIRST_VALUE(MAX(a) OVER (PARTITION BY a)) OVER (ORDER BY a) AS x FROM t1
 ERROR HY000: Window functions can not be used as arguments to group functions.
 DROP TABLE t1;
 #
+# MDEV-12059: Assertion `precision > 0' failed with a window function or window aggregate function
+#
+CREATE TABLE t1 (d DECIMAL(1,0) UNSIGNED);
+INSERT INTO t1 VALUES (1),(2);
+SELECT MIN(d) OVER () FROM t1;
+MIN(d) OVER ()
+1
+1
+DROP TABLE t1;
+#
 # End of 10.2 tests
 #

mysql-test/t/win.test

@@ -2472,6 +2472,15 @@ SELECT NTILE(MAX(a) OVER (PARTITION BY a)) OVER (PARTITION BY a ORDER BY b) FROM
 SELECT FIRST_VALUE(MAX(a) OVER (PARTITION BY a)) OVER (ORDER BY a) AS x FROM t1 GROUP BY a;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-12059: Assertion `precision > 0' failed with a window function or window aggregate function
+--echo #
+
+CREATE TABLE t1 (d DECIMAL(1,0) UNSIGNED);
+INSERT INTO t1 VALUES (1),(2);
+SELECT MIN(d) OVER () FROM t1;
+DROP TABLE t1;
+
 --echo #
 --echo # End of 10.2 tests
 --echo #

sql/item_windowfunc.h

@@ -953,6 +953,7 @@ class Item_window_func : public Item_func_or_sum
   bool fix_length_and_dec()
   {
     decimals = window_func()->decimals;
+    unsigned_flag= window_func()->unsigned_flag;
     return FALSE;
   }